1. Field of the Invention:
The invention relates to a cooling system of a printed board on which a plurality of electronic devices are mounted.
2. Related Art:
As an integrated circuit (hereinafter referred to as IC) which is mounted on a printed board is becoming denser, a heating value of the IC, namely, the amount of heat generated in the IC increases. Accordingly, it is necessary to forcibly cool the IC.
An example of a conventional cooling system of a printed board is described with reference to FIG. 5 and FIG. 6.
FIG. 5 is an exploded perspective view of a conventional cooling system of a printed board. In FIG. 5, the cooling system of a printed board comprises an electronic device 31, a cylindrical thermal conduction body 32, a spacer 33, a coil spring 34, a cooling block 35, cooling pipes 36, and screws 37.
A thermal conductivity compound 39a is applied onto the upper surface of a package portion 31a of the electronic device 31, and a thermal conductivity compound 39b is applied onto an insertion hole 35a provided in the cooling block 35 through which the thermal conduction body 32 is inserted at the portion where it contacts the thermal conduction body 32. The cooling block 35 is fixed to a printed board 38 by way of the spacer 33.
Screw holes 35b are provided on the upper surface of the cooling block 35. Both ends of the coil spring 34 are attached to the cooling block 35 by two screws 37. Owing to a tensile strength of the coil spring 34, the bottom surface of the cylindrical thermal conduction body 32 is pressed against the upper portion of the package portion 31a of the electronic device 31 by way of the thermal conductivity compound 39a.
FIG. 6 is a view for showing a state of mounting the conventional cooing system. In FIG. 6, the printed board 38 comprises a connector 41, guard rails 42, a fixed block 43, closing type couplers 44 and a pulling plate 45. The cooling pipes 36 through which a refrigerant 40 flows are fixed to the fixed block 43 which is fixed to the pulling plate 45 provided on the edge of the printed board 38. When the refrigerant 40 is forced to flow through the cooling pipes 36, the cooling block 35 around the cooling pipes 36 is cooled so that the electronic device 31 and printed board 38 are cooled by way of the cylindrical thermal conduction body 32.
Since a plurality of electronic devices 31 are varied in height, a thermal conductivity gel or a contactor such as a spring or the like is needed for absorbing the variation in height between the bottom surface of the cylindrical thermal conduction body 32 and the upper surface of the package portion 31a of the electronic device 31. However, as the heating density of the electronic device 31 increases, the thermal resistance of the thermal conductivity gel or the contactor such as a spring increases so that the reduction of variation in temperature generated in the electronic device 31 becomes difficult,.
Further, if failed electronic devices are produced on the printed board 38 on which the electronic devices are mounted, such failed electronic devices need to be inspected or replaced individually with other ones. Since the cooling part (cooling block shaft 35) covers the upper surface of the electronic device 31, when the electronic devices are inspected or replaced with other ones, the inspection has been difficult or an entire cooling part needed to be detached or removed for the replacement of the electronic devices. Accordingly, it take many steps for inspection, replacement or re-assembly.
Further, the conventional cooling system was high in packaged height and needed a heavy cooling block 35.